The increasing use of pipes known as "premium tubulars" in the construction of oil and gas wells has made it desirable to develop jaws which do not or only minimally damage the surface of the tubulars. Such jaws, which are generally referred to as "non-marking jaws" usually comprise an elastomeric material the pipe gripping surface of which may be coated with fine abrasive material to improve the grip.
Various means are used for applying such jaws to a pipe. In one known arrangement a multiplicity of hydraulic cylinders are provided which, in use, surround the tubular to be gripped and apply a generally uniform pressure to the jaws.
Whilst this arrangement provides the necessary gripping force it is relatively expensive to manufacture, operate and maintain. Furthermore, it relies on a convenient supply of hydraulic fluid being available.
Various mechanical arrangements are known for applying conventional jaws to conventional tubulars. Essentially, these mechanical arrangements are designed to press teeth on the jaw into the conventional tubular to obtain the necessary grip. These mechanical arrangements are designed to provide substantial radial force over a small area and are not suitable for use with non-marking jaws which ideally require to be applied with a generally uniform radially inward pressure.
At least preferred embodiments of the present invention aim to achieve this objective.